Pressure controllers/calibrators set and/or measure pressures in components, such as test devices, manifolds, and volumes. A typical prior art pressure controller/calibrator 100 used to set and measure the pressure of a gas in a test device is shown in FIG. 1. In particular, FIG. 1 shows a test volume 102 having an inlet port 112, an outlet port 142, and a test port 170. The inlet port 112 is connected to an inlet valve 111, which is connected to a supply pressure (not shown) through a supply port 110. The outlet port 142 is connected to an outlet valve 141, which is connected to an exhaust pressure (not shown) through an exhaust port 140. The supply pressure supplies pressure to the test volume 102, and the exhaust pressure removes pressure from the test volume 102. To increase pressure to the test volume 102, the inlet valve 111 may be opened, and to decrease pressure to from the test volume 102, the outlet valve 141 may be opened. However, to achieve small increases in pressure within the test volume 102, often the inlet valve 111 is pulse width modulated at varying widths and the outlet valve 141 is pulsed at a fixed width and rate. Conversely, to achieve small decreases in pressure within the test volume 102 the outlet valve 141 is pulsed width modulated at varying widths and the inlet valve 111 is pulsed at a fixed width and rate. The test port 170 is connected to a device under test (not shown). In addition, the test port 170 may be connected to a transducer and electronics (not shown) that drive the inlet and outlet valves 111, 141.
The supply pressure is typically greater than the highest pressure to be controlled in the test volume 102. For instance, the supply pressure may be ten percent greater than the pressure to be controlled in the test volume 102. The outlet valve 141 is connected to an exhaust pressure having a lower pressure than the test volume 102 through the exhaust port 140, which releases pressure from the test volume102. Typically, the exhaust pressure is atmosphere or a vacuum.
As stated above, the pressure in the test volume 102 is set by controlling the opening and closing of the inlet valve 111 and the outlet valve 141. Therefore, the differential pressure across the inlet valve 111, referred herein as inlet differential pressure, varies depending on the supply pressure and the test pressure within the test volume 102. Similarly, the differential pressure across the outlet valve 141, referred herein as outlet differential pressure, varies depending on the exhaust pressure and the test pressure in the test volume 102. In some instances, such as for high test volume pressures, the inlet differential pressure and the outlet differential pressure can deviate by three orders of magnitude or more throughout the controlled pressure range of the test volume 102.
High differential pressures require a large force to open the valves 111, 141. As a result, valves used in these pressure controllers are typically very large, consume excessive power, and often exhibit a slow response time. In addition, due to the large differential pressure across each valve 111, 141, the control precision of the valves 111, 141 are limited, thus providing a reduction in the stability of the pressure supplied to test volume 102. Furthermore, for the valves 111, 141 to produce bubble tight seals, valve poppets are typically manufactured from a soft elastomer that conforms to the seat. However, the combination of soft materials and high fluid velocities discussed above often results in premature wear of the valve poppets.
More recently, pressure controllers/calibrators comprising differential pressure regulators have been used to reduce the differential pressure applied to the inlet and outlet valves. FIG. 2 shows a pressure controller/calibrator 200 that includes such a configuration. The pressure controller 200 includes a test volume 202, a supply port 210, an inlet port 212, a test port 270, an outlet port 242, and an exhaust port 240 similar to those shown in FIG. 1. The pressure controller 200 of FIG. 2 differs from that in FIG. 1 by having a supply differential pressure regulator 201 placed between the inlet valve 211 and the supply port 210, and an exhaust differential pressure regulator 241 placed between the outlet valve 241 and the exhaust port 240. Between the supply regulator 201 and the inlet valve 211 is a high port 214, and between the exhaust regulator 241 and the outlet valve 241 is a low port 244. A supply feedback path 272 connects the test volume 202 with the supply regulator 201. Similarly, an exhaust feedback path 274 connects the test volume 202 with the exhaust regulator 241. The supply and exhaust feedback paths 272, 274 provide feedback regarding the pressure in the test volume 202.
The supply and exhaust differential regulators 201, 241 provide a low and relatively constant differential pressure across the inlet and outlet valves 211, 241, respectively. For instance, the supply differential pressure across the inlet valve 211 is the difference in pressure between the high port 214 and the inlet port 212. Similarly, the exhaust differential pressure across the outlet valve 241 is the difference in pressure between the low port 244 and the outlet port 242. These fixed, low differential pressures across the valves 211, 241 results in lower, more consistent flow rates through the valves 211, 241. Thus, improving the stability of the differential pressure across the control valves enhances the control precision of the system over the prior art shown in FIG. 1.
Pressure drop across the supply regulator 201 and the exhaust regulator 241 are typically large. For instance, the pressure at the supply port 210 is typically much higher than the pressure at the high port 214 and the pressure at the exhaust port 240 is typically much lower than the pressure at the low port 244. However, because regulators 201 and 241 are not directly responsible for the control precision in the test volume 202, they may be constructed more robustly to withstand the effects of higher supply and exhaust pressures. For instance, the regulators 201, 241 utilize metal on metal seats (not shown), which are more resistant to wear than the soft elastomer seats used in the prior art. However, the metal on metal seals result in some leakage. Therefore, a bypass path 280 that connects the high port 214 with the low port 244 is provided to prevent build up of pressure at the high port 214. The bypass path 280 includes a restriction 282 to limit the flow through the bypass path 280. The conductance of the bypass restriction 282 is sized to tolerate some leakage through the metal to metal seals. Because flow through the bypass 282 wastes supply fluid, leakage through seats 222 and 253 of prior art should be minimized.
Differential regulators of current art, like the regulators 201 and 241 shown in FIG. 2, are not capable of withstanding higher pressures, such as pressures greater than 10 MPa, without increasing wall thicknesses and screw sizes. Such modifications would make the regulators excessively heavy, large and expensive. In particular, because each diaphragm is held together between two flanges secured by screws, the clamping of the screws limits the maximum pressure the regulators can withstand. Above 10 MPa the regulators 201, 241 leak to atmospheric pressure on both sides of the diaphragm, thwarting the ability of the system to maintain a stable test pressure.
Diaphragms within differential regulators of prior art, like the diaphragms 280 and 285 shown in FIG. 2, are susceptible to damage caused by inadvertent overpressure events. For example, if supply pressure is inadvertently removed from the supply port 210 while high pressure is contained in the test volume 202, fluid will leak through the metal to metal seal of seat 253 and out the exhaust port 240. This leaves high pressure above the diaphragms 280 and 285 with low pressure below the diaphragms. This high differential pressure leads to damage of seat 253 and rupture of diaphragms 280 and 285.
Therefore, there is a need for a regulator that can operate at high pressures without requiring the regulator to become too bulky and heavy, and provides protection for the diaphragm and seats, reduces the amount of gas lost through the bypass path, and prevents leaks to atmosphere and within the system.